The objective of this study is to determine the efficacy of an intervention for increasing theory of mind (ToM), [social competence (SC), and emotion understanding (EU)] for low-income preschoolers via storybook interactions focused on characters and their mental states. ToM refers to the understanding of ourselves and other people as mental beings. A key ToM achievement is false belief understanding (FBU), which is the realization that events in the world can be represented correctly or incorrectly in one's mind. This topic is important as researchers have found lags in FBU in low-income preschoolers, and because FBU is related to aspects of school readiness [in low-income children, such as SC and EU (Weimer & Guajardo, 2005).] Researchers have demonstrated the efficacy of training FBU through storybook interactions (e.g., Guajardo & Watson, 2002); however, these studies were motivated to answer the theoretical question of whether language is causally related to FB using samples of children who are not at risk for delay in FBU. [Researchers often conceptualize both EU and FBU as part of ToM (Ensor & Hughes, 2008), and both are related to adults' mental state talk with children (Garner et al., 1997; Ruffman et al., 2002.] Thus, the proposed study has the primary goal of demonstrating the efficacy of intervention promoting [ToM through talk about mental states (beliefs, emotions)] in low-income children as there is no published research on ToM interventions in this population. This study will also improve upon the existing training studies by 1) assessing long-term consequences of ToM intervention, 2) assessing whether ToM intervention leads to increases not only in FBU, but also SC, [and EU] and 3) including control groups that will further clarify the benefit of a ToM intervention in the context of storybook reading. In total, two research questions are addressed: 1) What is the efficacy of a ToM intervention for low-income preschoolers FBU in the short-term and long-term? and 2) Does ToM intervention transfer to children's SC [and EU in the short-term and long-term]? A pre-test-post-test multigroup research design will be used in which low-income preschoolers (N=99) will be randomly assigned to an experimental group, a storybook control group (treated control), or a non- treatment control group. The experimental group will engage in storybook interactions in which discussions regarding characters and their mental states are embedded. The storybook control group will be read the same stories without such discussions, whereas the non-treatment control group will not participate in storybook interactions. Children's FBU, [SC, and EU] at pre-test and 2 post-tests will be assessed to determine the efficacy of the intervention. The first question of this study will be examined by determining whether the intervention has an effect on children's FBU relative to treated and non-treated controls immediately after intervention as well in the long-term (3 months later). To address the transfer of the intervention to children's SC [and EU, these skills will also be assessed at both post-tests.] PUBLIC HEALTH RELEVANCE: The proposed study will determine causally interpretable impacts of theory of mind (ToM) intervention for low- income preschoolers. ToM understanding-the understanding of ourselves and others as mental beings-is related to children's social competence, which is an important aspect of school readiness. Presently, educators and other professionals who desire to improve ToM development among high-risk populations have limited evidence-based resources to draw from; thus, it is important to demonstrate specific ways in which ToM understanding can be improved in this population.